Methods and systems for operating and maintaining a downhole wireless network

ABSTRACT

Disclosed herein are methods and systems for operating and maintaining downhole wireless networks. The methods and systems utilize a downhole tool, such as a downhole tool comprising a communications device, to perform maintenance on the downhole wireless network, and for overcoming and/or correcting communications errors along the network. The downhole tool may also be used for updating and reprograming communication nodes in the downhole wireless network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 62/611,864, filed Dec. 29, 2017 entitled “Method and System for Operating and Maintaining a Downhole Wireless Network,” the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present disclosure relates to methods and systems for operating and maintaining downhole wireless networks. In particular, the present disclosure relates to methods and systems that utilize a downhole tool to replace, repair, and/or maintain communications nodes in a downhole wireless network.

BACKGROUND

In the oil and gas industry, various communications systems have been introduced for monitoring downhole conditions and hydrocarbon production operations. For example, various wired and wireless technologies have been proposed to collect data from the downhole environment and transmit it to the operator at the surface.

As an example, wireless telemetry systems, such as downhole wireless networks, have been proposed. The wireless telemetry system may include a network of various communications nodes that exchange information with each other to manage data communication within the wellbore. Some wireless telemetry systems operate using radio transmissions. However, the use of radio transmissions may be impractical or unavailable in certain wellbore environments or during certain operations within the wellbore. Other wireless telemetry systems may utilize an acoustic wireless network that transmit acoustic signals, such as vibrations, via a tone transmission medium. In either systems, there are typically a plurality of communications nodes spaced-apart along the length of a tubular member within the wellbore.

Throughout the lifetime of the operation of the wireless telemetry system, there can be difficulties with the reliability and accuracy of the network. For example, the network can become severed if one or more communications nodes becomes unresponsive or fails to properly transmit signals to the next node. As another example, the network may become less reliable due to the continually changing and unpredictable conditions within the wellbore. That is, the acoustic conditions within the wellbore may be effected by formation variations, cementation variations, varying fluid compositions within the wellbore, fracking operations, and/or hydrocarbon production operations. The changes in the acoustic conditions can affect the ability of the nodes to properly communicate with one another via acoustic transmissions.

Thus, there is a need for methods and systems to aid in the diagnosis of errors in the downhole wireless network, and/or for methods and systems to aid in the reliable operation and maintenance of the downhole wireless network. Further, there is a need for methods and systems for repairing or healing a downhole wireless network that has begun to operate unreliably or has become severed.

Background references may include (i) U.S. Pat. Nos. 5,924,499; 6,462,672; 6,899,178; 6,909,667; 6,912,177; 7,228,902; 7,249,636; 7,477,160; 8,115,651; 9,557,434; 9,631,485; 9,759,062; 9,816,373; 9,863,222; 9,879,525; 10,100,635; and 10,132,149 (ii) U.S. Patent Application Publication Nos. 2008/0030365; 2015/0292319; 2015/0300159; 2015/0354351; 2016/0076363; and 2016/0215612; 2018/0058191; 2018/0058198; 2018/0058202; 2018/0058203; 2018/0058204; 2018/0058205; 2018/0058206; 2018/0058207; 2018/0058208; 2018/0058209; 2018/0066510; and (iii) U.S. patent application Ser. No. 15/666334.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side, cross-sectional view of an illustrative wellbore having been completed as a cased hole completion. A series of communications nodes are placed along a casing string as part of a downhole telemetry system in the wellbore.

FIG. 2A is a schematic of an exemplary communications node. FIG. 2B is a cross-sectional view of an exemplary communications node taken along the longitudinal axis of the node.

FIG. 3A is an illustration of a severed downhole wireless network, and FIG. 3B is an illustration of using a hydrophone to reconnect the severed downhole wireless network.

FIG. 4 is an illustrative ultrasonic hydrophone that may be used in the methods and systems described herein.

FIG. 5 is a flowchart of an illustrative embodiment of the methods described herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

Various specific embodiments, versions, and examples of the invention will now be described, including preferred embodiments and definitions that are adopted herein for purposes of understanding the claimed invention. While the following detailed description gives specific preferred embodiments, those skilled in the art will appreciate that these embodiments are exemplary only, and that the invention can be practiced in other ways. For purposes of determining infringement, the scope of the invention will refer to any one or more of the appended claims, including their equivalents, and elements or limitations that are equivalent to those that are recited. Any reference to the “invention” may refer to one or more, but not necessarily all, of the inventions defined by the claims.

Terminology

Various terms as used herein are defined below. To the extent a term used in a claim is not defined below, it should be given the broadest possible definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent.

As used herein, the term “communication node” may be used to refer to a topside communication node, an intermediate communication node, and/or a sensor communication node.

As used herein, the term “conduit” refers to a tubular member forming a physical channel through which something is conveyed. The conduit may include one or more of a pipe, a manifold, a tube or the like, or the liquid contained in the tubular member.

As used herein, the term “determining” encompasses a wide variety of actions and may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, database, or other data structure), ascertaining, and the like. Determining may also refer to resolving, selecting, choosing, establishing, and the like.

As used herein, the term “fluid” refers to gases, liquids, and combinations of gases and liquids, as well as to combinations of gases and solids where the gas is the majority component of the fluid, and combinations of liquids and solids where the liquid is the majority component of the fluid.

As used herein, the term “fluid flow measurement” refers to measuring one or more fluid flow parameters including, but not limited to, one or more of velocity, volume, pressure, resistivity, vibration, pressure drop, temperature, impedance, attenuation, density, viscosity, flow type, and the like. Such measurements can be used to determine, for example, fluid viscosity, fluid composition, phase fraction, annular distribution of flows and phases across a cross-section, flow-rate, and the like.

As used herein, the term “flow” refers to a current or stream of a fluid. Flow can be understood as the quantity of a fluid that passes a point per unit of time. Factors that affect flow can include, but are not limited to, pressure (e.g., flow is directly proportional to the pressure difference across a tube), length (e.g., flow is inversely proportional to the length of a tube), viscosity (e.g., flow is inversely proportional to the viscosity of the fluid), temperature of the fluid, fluid density, compressibility of the fluid, number of phases of the fluid (i.e., single phase or multiphase), friction, and chemical properties of the fluid.

As used herein, the term “formation” refers to any definable subsurface region. The formation may contain one or more hydrocarbon-bearing layers, one or more non-hydrocarbon containing layers, an overburden, and/or an underburden of any geologic formation.

As used herein, the term “hydrocarbon” refers to an organic compound that includes primarily, if not exclusively, the elements hydrogen and carbon. Hydrocarbons generally fall into two classes: aliphatic hydrocarbons, also known as straight chain hydrocarbons, and cyclic hydrocarbons, also known as closed ring hydrocarbons. While hydrocarbons generally comprise the elements hydrogen and carbon, in some embodiments hydrocarbons may also comprise minor amounts of other elements or compounds, such as, but not limited to, halogens, metallic elements, nitrogen, oxygen, sulfur. Examples of hydrocarbon-containing materials include any form of natural gas, oil, coal, and bitumen.

As used herein, the term “condensable hydrocarbons” refers to those hydrocarbons that condense at about 15° C. and one atmosphere of pressure. Condensable hydrocarbons may include, for example, a mixture of hydrocarbons having carbon numbers greater than 3.

As used herein, the term “hydrocarbon fluids” refers to a hydrocarbon or mixtures of hydrocarbons that are gases or liquids. For example, hydrocarbon fluids may include a hydrocarbon or mixtures of hydrocarbons that are gases or liquids at formation conditions, at processing conditions, or at ambient conditions (i.e., at about 20° C. and 1 atm pressure). Hydrocarbon fluids may include, for example, oil, natural gas, gas condensates, coal bed methane, shale oil, pyrolysis oil, and other hydrocarbons that are in a gaseous or liquid state.

As used herein, “hydrocarbon exploration” refers to any activity associated with determining the location of hydrocarbons in subsurface regions. Hydrocarbon exploration normally refers to any activity conducted to obtain measurements through acquisition of measured data associated with the subsurface formation and the associated modeling of the data to identify potential locations of hydrocarbon accumulations. Accordingly, hydrocarbon exploration may include acquiring measurement data, modeling of the measurement data to form subsurface models, and determining the likely locations for hydrocarbon reservoirs within the subsurface. The measurement data may include seismic data, gravity data, electromagnetic data, geochemical data, and the like. In some embodiments, hydrocarbon exploration activities may also include drilling exploratory wells, obtaining core samples or other fluid samples, and acquiring measurement data from the core or fluid samples.

As used herein, “hydrocarbon development” refers to any activity associated with the planning of extraction and/or access to hydrocarbons in subsurface regions. Hydrocarbon development normally refers to any activity conducted to plan for access to and/or for production of hydrocarbons from the subsurface formation and the associated modeling of the data to identify preferred development approaches and methods. For example, hydrocarbon development may include modeling of the subsurface formation and extraction planning for periods of production, determining and planning equipment to be utilized and techniques to be utilized in extracting the hydrocarbons from the subsurface formation, and the like.

As used herein, “hydrocarbon production” refers to any activity associated with extracting hydrocarbons from subsurface locations, such as a well or other opening. Hydrocarbon production activities may refer to any activity conducted to form the wellbore along with any activity in or on the well after the well is completed. Accordingly, hydrocarbon production activities includes not only primary hydrocarbon extraction, but also secondary or tertiary production techniques, such as injection of gas or liquid for increasing drive pressure, mobilizing the hydrocarbons or treating the hydrocarbons by, for example, chemicals, hydraulic fracturing the wellbore to promote increased flow, well servicing, well logging, and other well and wellbore treatments.

As used herein, “monitored section” and “monitored sections” refer to locations along the tubular members that include sensors and/or regions of interest.

As used herein, “unmonitored section” and “unmonitored sections” refer to locations along the tubular members that do not include sensors and/or are not regions of interest.

As used herein, the term “multi-zone fluid producing well” or “multi-zone production well” refers to a hydrocarbon-producing well that includes at least two production zones.

As used herein, the terms “near real-time” and “real-time” are used interchangeably and refer to the systems and methods where the time delay introduced, by automated data processing or network transmission, between the occurrence of an event and the use of the processed data, such as for display or feedback and control purposes. For example, a near-real-time or real-time display depicts an event or situation as it existed at the current time minus the processing time, as nearly the time of the live event. The time delay with regard to “near real-time” or “real-time” can be on the order of several milliseconds to several minutes, several milliseconds to several seconds, or several seconds to several minutes.

As used herein, the terms “optimal”, “optimizing”, “optimize”, “optimality”, “optimization”, as well as derivatives and other forms of those terms and linguistically related words and phrases, as used herein, are not intended to be limiting in the sense of requiring the present invention to find the best solution or to make the best decision. Although a mathematically optimal solution may in fact arrive at the best of all mathematically available possibilities, real-work embodiments of optimization routines, methods, models, and processes may work towards such a goal without ever actually achieving perfection. Accordingly, one of ordinary skill in the art having benefit of the present disclosure will appreciate that these terms, in the context of the scope of the present invention, are more general. The terms may describe one or more of: 1) working towards a solution which may be the best available solution, a preferred solution, or a solution that offers a specific benefit within a range of constraints; 2) continually improving; 3) refining; 4) searching for a high point or a maximum for an objective; 5) processing to reduce a penalty function; 6) seeking to maximize one or more factors in light of competing and/or cooperative interests in maximizing, minimizing, or otherwise controlling one or more other factors, etc.

As used herein, the term “potted” or “potting” refers to the encapsulation of electrical components with epoxy, elastomeric, silicone, or asphaltic or similar compounds for the purpose of excluding moisture or vapors. Potted components may or may not be hermetically sealed.

As used herein, the term “produced fluids” and “production fluids” refer to liquids and/or gases removed from a subsurface formation. Produced fluids may include both hydrocarbon fluids and non-hydrocarbon fluids. For example, produced fluids may include natural gas, pyrolyzed shale oil, synthesis gas, a pyrolysis product of coal, carbon dioxide, hydrogen sulfide, and water (including steam).

As used herein, the term “production casing” includes a liner string or any other tubular body fixed in a wellbore along a zone of interest.

As used herein, the term “production optimization” refers to any method, device, control device, valve, chemical, metrics, data analysis, and/or system, that can be used to improve hydrocarbon fluid production efficiency, hydrocarbon fluid production rates, hydrocarbon fluid recovery, produced gas/oil ratio, hydrocarbon fluid phase, utilization of the production plant to achieve higher throughput, water-cut, workovers, etc. Production optimization can be real-time production optimization including partial or complete automation, and/or optimization of control settings. Production optimization can be accomplished, for example, but not limited to, chemically by preventing or inhibiting scale, paraffin, asphaltene, and/or corrosion using inhibitors of one or more thereof; extending field life using for example, defoamers, emulsifiers, foamers, flow improvers, tracer dyes, and/or water clarifiers, acidizing, etc.; reinstating or improving flow performance chemically using, for example, dissolvers, cleaners, scavengers, adsorbents, water flooding, CO2 flooding, etc.; mechanically, for example, but not limited to artificial lift, using, for example, pumps, including but not limited to, electric submersible pumps, gas lift, horizontal surface pumps, subsea lift systems, dewatering pump systems, geothermal pump systems, industrial pump systems, etc.; gas/water injection optimization; tubing size optimization; perforation optimization; nitrogen circulation; and the like. In certain cases, production optimization may include sealing a lost circulation zone.

Production optimization can include, but is not limited to, one or more of the following: equalizing reservoir inflow along a length of the wellbore, partially choking flow, delaying water or gas breakthrough by reducing annular velocity across a selected interval, e.g., such as the heel of a horizontal well, adjusting flow from individual zones of a production well including one or more zones of a multi-zone production well, e.g., that are over- or under-pressured, slowing water, and/or gas encroachment, and reducing the amount of bypassed reserves by equalizing a pressure drop along a length of a wellbore, e.g., so as to promote uniform flow of oil and gas through a formation so that the arrivals of water and gas are delayed and simultaneous. Production optimization can be accomplished using, for example, but not limited to, one or more of control devices including for example, ICDs that can be used to manage fluid outflow in injection wells. ICDs can be placed both in injection and producer wells; or more remotely actuated downhole valves to shut off or reduce fluid flow from one or more well production zones; outflow control devices, valves, and corresponding actuation devices, wellbore isolation devices including for example, tool seals, packers, cement plugs, bridge plugs, chemical control devices, and the like.

As used herein, the term “sealing material” refers to any material that can seal a cover of a housing to a body of a housing sufficient to withstand one or more downhole conditions including but not limited to, for example, temperature, humidity, soil composition, corrosive elements, pH, and pressure.

As used herein, the term “sensor” includes any sensing device or gauge, such as an electrical device or gauge. The sensor may be capable of monitoring and/or detecting and/or measuring a fluid flow parameter, including for example, but not limited to pressure, pressure drop, temperature, fluid flow, fluid type, volumetric flow, fluid velocity, vibration, resistivity, impedance, attenuation, or other fluid flow data. Alternatively, the sensor may be a position or location sensor.

As used herein, the term “subsurface” refers to the region occurring below the Earth's surface. For example, the subsurface may be beneath the top surface of any mass of land at any elevation or over a range of elevations, whether above, below, or at sea level, and/or beneath the floor surface of any mass of water, whether above, below, or at sea level.

As used herein, the term “topside communication node” as used herein, refers to a communication node that can be located topside, proximate a surface. The topside communication node can be a virtual topside communication node that can be located subsurface or downhole, and can function as a topside node. The virtual topside communication node can be located, for example, at locations including but not limited to, the bottom of a vertical section, e.g., at the start of a deviated section, for example, in order to communicate with multi-zone horizontal sections of a multi-zone well. Data can be brought to the surface, e.g., to a receiver located at the surface, using, for example, but not limited to, one or more of a wireless connection, e.g., an RF wireless connection, a cable, a fiber optic cable, and the like.

As used herein, the terms “tubular member” or “tubular body” or “subsurface pipe” refer to any pipe, such as a joint or casing, a portion of a liner, a drill string, a production tubing, an injection tubing, a pup joint, a buried pipeline, underwater piping, or above-ground piping.

As used herein, the term “wellbore” refers to a hole in the subsurface made by drilling or insertion of a conduit into the subsurface. A wellbore may have a substantially circular cross section or other cross-sectional shape. As used herein, the term “well”, when referring to an opening in the formation, may be used interchangeably with the term “wellbore”.

As used herein, the term “well data” may include seismic data, electromagnetic data, resistivity data, gravity data, well log data, core sample data, and combinations thereof. The well data may be obtained from memory or from the equipment in the wellbore. The well data may also include the data associated with the equipment installed within the wellbore and the configuration of the wellbore equipment. For example, the well data may include the composition of the tubular members, thickness of the tubular members, length of the tubular members, fluid composition within the wellbore, formation properties, and/or other suitable properties associated with the wellbore.

As used herein, the terms “zone” or “zone of interest” refer to a portion of a formation containing hydrocarbons. Zones of interest may also include formations containing brines or useable water which are to be isolated.

Description

The present invention is related to the use of downhole telemetry systems, such as downhole wireless networks, and in particular, to methods and systems for operating and maintaining such networks. The downhole wireless network employs a series of communication nodes spaced along a tubular member in a wellbore. The communication nodes operate to wirelessly transmit signals that represent packets of information (e.g., information about one or more conditions within the wellbore), in a node-to-node manner, and to deliver the information from the subsurface to the topside. Over the operational life of the network, there may be become instances where the network does not operate properly. For example, there may be a communications failure between two or more nodes. As another example, over time the acoustic environment in the wellbore may change and there may be a desire to reprogram nodes to be more accurate and reliable. The present methods and techniques provide means for performing maintenance on the downhole wireless network, and for overcoming and/or correcting communications errors along the network and for updating and reprograming nodes in the network.

Thus, in one or more embodiments, the methods and systems described herein may utilize a downhole tool to obtain data from a portion of the network where communication has been lost or severed. For example, the methods may comprise detecting a communications error in the downhole wireless network; identifying one or more communication nodes that are no longer transmitting data; lowering the downhole tool through the wellbore to the location of the communication nodes that are no longer transmitting data; and collecting data from the communication node below the communication node that is no longer transmitting; and using the downhole tool to transmit the data to the surface. In some embodiments, the methods and systems may further comprise utilizing the downhole tool to diagnose the error with the malfunctioning communication node. If the error, is due to a problem with the programming of the node, the downhole tool can transmit a new program to the malfunctioning communication node to correct the error.

The present methods and techniques may be further understood with reference to the Figures, which are described further below. In certain figures (such as FIG. 1), the top of the drawing page is intended to be toward the earth surface and the bottom of the drawing page toward the well bottom. While wells are commonly completed in a substantially vertical orientation, it is understood that wells may also be inclined and or horizontally completed (as shown in FIG. 1). Thus, when the descriptive terms “up” and “down” or “upper” and “lower” or similar terms are used in reference to a drawing or in the claims, they are intended to indicate relative location on the drawing page or with respect to well descriptions, and are not necessarily an absolute orientation in the ground, as at least some embodiments of the present inventions have utility no matter how the wellbore is oriented. Thus, the present inventions may have equally utility in vertically completed wells, horizontally completed wells, or in multi-lateral deviated wells as further described herein.

The present methods and techniques described herein may also be better appreciated with reference to flow diagrams (such as those in FIG. 5). While for purposes of simplicity of explanation, the illustrated methodologies may be shown and described as a series of blocks in FIGS. 5, it is to be appreciated that the methodologies are not limited by the order of the blocks, as some blocks can occur in different orders and/or concurrently with other blocks from that shown and described. Moreover, less than all the illustrated blocks may be required to implement various embodiments of an example methodology. Blocks may be combined or separated into multiple components. Furthermore, additional and/or alternative methodologies can employ additional blocks not shown herein. While the figures illustrate various actions occurring serially, it is to be appreciated that various actions could occur in series, substantially in parallel, and/or at substantially different points in time.

FIG. 1 is a side, cross-sectional view of an illustrative well site 100. The well site 100 includes a wellbore 150 that penetrates into a subsurface formation 155. The wellbore 150 has been completed as a cased-hole completion for producing hydrocarbon fluids. The well site 100 also includes a well head 160. The well head 160 is positioned at an earth surface 101 to control and direct the flow of formation fluids from the subsurface formation 155 to the surface 101.

The well head 160 may be any arrangement of pipes or valves that receive reservoir fluids at the top of the well. In the arrangement of FIG. 1, the well head 160 is a so-called Christmas tree. A Christmas tree is typically used when the subsurface formation 155 has enough in situ pressure to drive production fluids from the formation 155, up the wellbore 150, and to the surface 101. The illustrative well head 160 includes a top valve 162 and a bottom valve 164. In some contexts, these valves are referred to as “master valves”. Other valves may also be used. In a subsea context, the wellhead may also include a lower marine riser package (not shown).

It is understood that rather than using a Christmas tree, the well head 160 may alternatively include a motor (or prime mover) at the surface 101 that drives a pump. The pump, in turn, reciprocates a set of sucker rods and a connected positive displacement pump (not shown) downhole. The pump may be, for example, a rocking beam unit or a hydraulic piston pumping unit. Alternatively still, the well head 160 may be configured to support a string of production tubing having a downhole electric submersible pump, a gas lift valve, or other means of artificial lift (not shown). The present invention is not limited by the configuration of production equipment at the surface unless expressly noted in the claims.

The wellbore 150 in FIG. 1 has been completed with a series of pipe strings, referred to as casing. First, a string of surface casing 110 has been cemented into the formation. Cement is shown in an annular bore 115 of the wellbore 150 around the surface casing 110. The cement is in the form of an annular sheath 112. The surface casing 110 has an upper end in sealed connection with the lower valve 164.

Next, at least one intermediate string of casing 120 is cemented into the wellbore 150. The intermediate string of casing 120 is in sealed fluid communication with the upper master valve 162. A cement sheath 112 is again shown in a bore 115 of the wellbore 150. The combination of the casing 110/120 and the cement sheath 112 in the bore 115 strengthens the wellbore 150 and facilitates the isolation of formations behind the casing 110/120.

It is understood that a wellbore 150 may, and typically will, include more than one string of intermediate casing 120. In some instances, an intermediate string of casing may be a liner. Some of the intermediate strings of casing may be only partially cemented into place, depending on regulatory requirements and the presence of migratory fluids in any adjacent strata.

Finally, a production string 130 is provided. The production string 130 is hung from the intermediate casing string 120 using a liner hanger 131. The production string 130 is a liner that is not tied back to the surface 101. Preferably, all of the production liner 130 is cemented in place. In the arrangement of FIG. 1, a cement sheath 132 is provided around the liner 130 along its entire length.

The production liner 130 has a lower end 134 that extends to an end 154 of the wellbore 150. For this reason, the wellbore 150 is said to be completed as a cased-hole well. In FIG. 1, the production liner 130 extends through a horizontal portion 190 of the formation 155. The horizontal portion 190 of the wellbore 150 typically extends for many hundreds of feet. For example the horizontal portion 190 may extend for over 250 feet, or over 1,000 feet, or even more than 5,000 feet. Extending the horizontal portion 190 of the wellbore 150 such great distances significantly increases the exposure of the formation 155 of the wellbore 150.

The formation 155 may be any hydrocarbon-bearing formation. However, in some embodiments, the formation may be a carbonate or sand formation having good consolidation but poor permeability, or may be a shale formation having low permeability. For example, in some embodiments, the formation may have a permeability of less than 100 milliDarcies (“mD”), or less than 50 mD, or less than 10 mD, or less than 1 mD. It is common for wells that are completed in so-called “tight” or “unconventional” formations to be completed horizontally as illustrated in FIG. 1. Horizontal completions not only dramatically increase exposure of the wellbore to the producing rock face, but also enable the operator to create fractures that are substantially transverse to the direction of the wellbore. Those of ordinary skill in the art may understand that a rock matrix will generally “part” in a direction that is perpendicular to the direction of least principal stress. For deeper wells, that direction is typically substantially vertical. While FIG. 1 illustrates a horizontally completed well, those skilled in the art would understand that the present methods and techniques would have equal utility in optimizing stimulation operations in other well arrangements, such as vertically completed wells or in multi-lateral deviated wells.

The wellbore 150 illustrated in FIG. 1 has been perforated 159 for a fracturing operation. That is, as part of the well completion process, the casing has been perforated, whereby lateral holes have been shot through the casing and the cement sheath surrounding the casing to allow hydrocarbon fluids to flow into the wellbore. Various techniques may be used for creating the perforations. Common techniques utilize a wellbore tool that includes a perforating gun, and optionally, a fracturing plug. The wellbore tool may be a wireline tool or may be an autonomous tool (i.e., a tool that does not require a wireline and is not mechanically tethered to equipment external to the wellbore).

The wellbore 150 comprises sets of perforations 159 are provided in three separate zones 102, 104, and 106. Each zone may be of any length, but generally each zone may represent, for example, a length of up to about 200 feet, or up to 100 feet, or up to 50 feet. In general, the length of each zone can depend on a number of factors, such as the type of rock material in the zone, the permeability of the zone, the porosity of the zone, and/or the hydrocarbon fluid composition in the zone. As described further below, the methods and techniques described herein may be used to determine the optimal length and spacing of desired fracturing zones. While only three sets of perforations 159 are shown, it is understood that the horizontal portion 190 may have many more sets of perforations 159 in additional zones.

The wellbore 150 of FIG. 1 also has a string of injection tubing 140. The injection tubing 140 extends from the well head 160 down to the subsurface formation 155. In the arrangement of FIG. 1, the injection tubing 140 terminates proximate an upper end of the subsurface formation 155. In operation, the operator may stimulate and treat each zone 102, 104, and 106 separately and sequentially. Therefore, it is understood that the injection tubing 140 can be pulled through the horizontal portion of the wellbore 150 so that the injection fluids may be injected through the perforations 159 in zones 102, 104, and 106 separately and sequentially as desired.

A packer 141 is provided at a lower end of the injection tubing 140. The packer 141 is set when an injection fluid, such as an acid and/or fracturing fluid, is being injected through a set of perforations 159. The packer 141 will be released when it is time to move the injection tubing 140 to a different zone, or to remove it from the wellbore 150 completely.

In preparation for the production of hydrocarbons, the operator may wish to stimulate the formation 155 by conducting an acidization operation. This serves to clean out residual drilling mud along both the wall of the borehole 115 and into the near-wellbore region (the region within formation 155 close to the production casing 130). An acidization operation can be done by injecting an acid solution down the wellbore and through the perforations. The use of an acidizing solution is particularly beneficial when the formation comprises carbonate rock. Thus, in some embodiments, the operator may inject a concentrated formic acid or other acidic composition into the wellbore, and direct the fluid into selected zones of interest. The acid helps to dissolve carbonate material, thereby opening up porous channels through which hydrocarbon fluids may flow into the wellbore. In addition, the acid helps to dissolve drilling mud that may have invaded the formation. The acidization may be conducted alone or in addition to a fracturing operation, such as before or after a fracturing operation.

In some embodiments, the operator may wish to fracture the formation 155. This is done by injecting a fracturing fluid under high pressure through the perforations 159 and into the formation 155. The fracturing process creates fractures 108 along the formation 155 to enhance fluid flow into the production casing 130. Where the natural or hydraulically-induced fracture plane(s) of a formation are vertical, a horizontally completed wellbore (portion 190) allows the production casing 130 to intersect multiple fracture planes. Hydraulic fracturing operations typically comprise injecting viscous fluids (usually shear thinning, non-Newtonian gels or emulsions) into the formation at such high pressures and rates that the reservoir rock fails and forms a network of fractures. The fracturing fluid is typically mixed with a granular proppant material such as sand, ceramic beads, or other granular materials. The proppant serves to hold the fracture(s) open after the hydraulic pressures are released. The combination of fractures and injected proppant helps increase the flow capacity of the treated reservoir.

While FIG. 1 illustrates a well that has been fractured by hydraulic fracturing operations, those skilled in the art would understand that the present methods and techniques would have equal utility in maintaining and operating downhole wireless networks in wellbores that have not undergone hydraulic fracturing operations.

A downhole telemetry system is provided at the well site 100 of FIG. 1. The telemetry system utilizes a series of communication nodes 180 arranged along the length of a conduit and/or tubular in the wellbore. In some embodiments, the communication nodes may be placed or positioned along the outer diameter of the casing strings 110, 120, and/or 130. In some embodiments, the communication nodes may be recessed within the pipe body, placed internally within the pipe body, at cross-sectional ends of the pipe joint, and/or positioned inside of the pipe through bore, and combinations thereof. For example, communication nodes may be placed on each pipe joint or casing joint, or may be placed at selected locations along every second or every third pipe joint. In some embodiments, some pipe joints receive two or more communication nodes.

Preferably, the communication node 180 is an independent wireless communication device that is designed to be attached to an external surface of the conduit or tubular member, but may also be attached to an inner surface, an end surface (e.g., on the cross-sectional end face of a connection), embedded within a wall of the conduit or tubular member, or combinations thereof. There are benefits to the use of an externally-placed communication nodes that use acoustic waves. For example, such a node will not decrease the effective inner diameter of the conduit or tubular member which could interfere with passing subsequent assemblies or tubulars through the internal bore of the conduit or tubular member. Further, installation and mechanical attachment of the communication node to the external surface can be readily assessed and adjusted.

The communication nodes are designed to attach to the wall of the conduit or tubular member, such as the casing or pipe. For example, the communication node may be pre-welded onto the wall of the conduit or tubular member. Alternatively, the communication node may be glued using an adhesive such as epoxy. In some embodiments, it may be preferred that the communication nodes are configured to be selectively attachable to and/or detachable from the conduit or tubular member by mechanical means at the well site. This may be done, for example, through the use of clamps. For example, a clamping system can be used that would allow a drilling or service company to mechanically connect/disconnect the communication nodes along the tubular body as the tubular body is being run into a wellbore.

In the arrangement of FIG. 1, the communication nodes 180 may represent a plurality of subsurface communication nodes 180. Each of the subsurface communication nodes 180 is configured to receive and then relay acoustic signals along the length of the wellbore 150, such as from the subsurface formation 155 up to the surface 101. The communication nodes 180 transmit acoustic signals. Preferably, the subsurface communication nodes 180 utilize two-way transceivers to receive and transmit signals as acoustic waves. The acoustic waves are preferably at a frequency of between about 50 kHz and 500 kHz, or from about 100 kHz to about 125 kHz.

The communication nodes also include one or more topside communication nodes 182. In FIG. 1 only one topside communication node is shown; however, in some embodiments, two or more topside communication nodes may be used. The topside communication node 182 is placed closest to the surface 101. The topside node 182 is configured to receive acoustic signals from the upper-most of the subsurface communication nodes 180. Thus, signals are delivered from the subsurface up to the topside communication node 182, in a node-to-node arrangement by the plurality of communication nodes 180. The topside communication node 182 is typically configured to receive the acoustic signals from the plurality of communication nodes 180 and convert the acoustic signals to electrical and/or optical signals which are then relayed on to a receiver 170 at the surface 101. The topside communication node 182 may be above grade (i.e., above the surface) or below grade (i.e., below the surface). In preferred embodiments, the topside communication node 182 is actually connected to the well head 160.

The well site 100 illustrates a receiver 170. The receiver 170 comprises a processor 172 that receives signals sent from the one or more topside communication nodes 182. The processor 172 may include discrete logic, any of various integrated circuit logic types, or a microprocessor. The receiver 170 may also include a screen and a keyboard 174 (either as a keypad or as part of a touchscreen). The receiver 170 may also be an embedded controller with neither screen nor keyboard which communicates with a remote computer via cellular modem, satellite, Wi-Fi, or telephone lines. In one aspect, the processor 172 is part of a multi-purpose “smart phone” having specific “apps” and wireless connectivity.

The signals may be received by the receiver 170 through a wire (not shown) such as a co-axial cable, a fiber optic cable, a USB cable, or other electrical or optical communications wire. Alternatively, the receiver 170 may receive the final signals from the topside node 182 wirelessly through modem or transceiver or other wireless communications link. In some embodiments, the receiver 170 may receive electrical signals via a so-called Class 1, Division 1 conduit, that is, a housing for a wire as defined by NFPA 497 and API 500 for operations in an electrically classified area. Alternatively, data can be transferred from the topside node to a receiver via an electromagnetic (RF) wireless connection. In some embodiments, infrared or microwave signals may also or alternatively be utilized.

The signals and data obtained from the various communication nodes may then be used by the wellbore operator to monitor and/or optimize the hydrocarbon development or hydrocarbon production operations with the wellbore. For example, the signals and data that are received may be beneficial for enhancing hydrocarbon operations, such as optimizing stimulation operations as described further below.

The communication nodes 180 in FIG. 1 may be of various configurations, such as the communication node 255 illustrated in FIG. 2A or communication node 200 illustrated in FIG. 2B. In general, the communication nodes comprise an elongated body that supports one or more power sources and an electro-acoustic transducer. The elector-acoustic transducer is associated with a transceiver that receives acoustic signals at a first frequency, converts the received signals into a digital signal, and transmits the acoustic signal at a second frequency to the next communication node. Thus, the elector-acoustic transducer in each node allows signals to be sent node-to-node up the wellbore as acoustic waves. Beneficially, the subsurface communication nodes do not require a wire or cable to transmit data to the surface.

FIG. 2A is a diagram of an exemplary communication node 255. The communication node 255 may include a housing 260 along with a central processing unit (“CPU”) 270; memory 275, which may include instructions or software to be executed by the

CPU 270; one or more encoding components 285; one or more decoding components 290; a power component 295; and/or one or more sensing components 280; all of which communicate via a bus 216.

The power component 295 is generally configured to provide power to the components within the communication node 255. The power component may include one or more batteries, capacitors, super-capacitors, fuel cells, or other energy storage components. The batteries and/or fuel cells may or may not be rechargeable.

The CPU 270 may be any general-purpose CPU, although other types of architectures of CPUs may be used as long as the CPU 270 supports the operations of the communication nodes described herein. In one or more embodiments, the CPU 270 may contain may contain one or more microprocessors and may be a system on chip (“SOC”), digital signal processor (“DSP”), application specific integrated circuit (“ASIC”), and/or field programmable gate array (“FPGA”). The CPU 270 may execute the various logical instructions to operate the communication node 255. For example, the CPU may execute machine-level instructions for performing processing of the data and/or signals as described herein.

The memory 275 may include random access memory (“RAM”), such as static RAM (“SRAM”), dynamic RAM (“DRAM”), synchronous DRAM (“SDRAM”), or the like, read only memory (“ROM”), such as programmable ROM (“PROM”), erasable PROM (“EPROM”), electronically erasable PROM (“EEPROM”), or the like. In addition, the memory 275 may include NAND flash and/or NOR flash.

To manage the communications, the communication node 255 utilize the one or more encoding components 285 and one or more decoding components 290 within the housing 260. The encoding components 285, which may include one or more transducers, may be disposed within the housing 260 and may be configured to generate acoustic tones and/or to induce an acoustic tone on a tone transmission medium. The one or more decoding components 290, which may include one or more transducers, may be disposed within the housing 260 and may be configured to receive acoustic tones from the tone transmission medium. The encoding 285 and decoding 290 components may include instructions stored in memory and utilized to perform the generation of the acoustic tones or decoding of the acoustic tones along with the compression or decompression of data packets into acoustic tones. In one or more embodiments, the encoding component 285 and the decoding component 290 may utilize the same transducer.

The one or more sensing components 280 may be configured to obtain sensing data (such as measurement data) and communicate the data to the transducer for communication to the other communication nodes. By way of example, the sensing components 280 may be configured to obtain pressure measurements, temperature measurements, fluid flow measurements, vibration measurements, resistivity measurements, capacitance measurements, strain measurements, acoustics measurements, stimulation and/or hydraulic fracture properties measurements, chemicals measurements, position measurements, and/or other suitable measurements. Additional examples of suitable sensing components are described with reference to FIG. 2B.

FIG. 2B provides another exemplary configuration of a communication node 200 and shows a cross-sectional view of the communication node 200 along its longitudinal axis. The communication node 200 includes a housing 210, such as a fluid-sealed housing. The housing 210 is designed to be attached to an outer wall of a joint of a wellbore conduit or tubular member as described above. The communication nodes may be specially designed to withstand the corrosion and environmental conditions (e.g., high temperature, high pressure) of the wellbore. For example, the communication nodes may comprise steel, fluid-sealed housings for holding the electronics (e.g., batteries and/or electro-acoustic transducers). In some embodiments, the steel material is a corrosion resistant alloy. In some embodiments, it may be desirable to metallurgically match the housing of the communication node with that of the conduit or tubular member to aid in avoiding galvanic corrosion at the coupling. In some embodiments, it may be desirable to fabricate the wall of the communication node from a material having a resonance frequency compatible with the resonance frequency of the tubular body. For example, the mechanical resonance of the wall 212 may be at a frequency contained within the frequency band used for the telemetry system.

The housing 210 includes an outer wall 212. The wall 212 is dimensioned to protect internal electronics for the communication node 200 from wellbore fluids and pressure. In some embodiments, the wall 212 may have a thickness of less than 0.5 inches, such as from 0.01 inch to 0.5 inches, or from about 0.01 inch to about 0.4 inch, or from 0.1 inch, to about 0.3 inch, or be about 0.2 inches (0.51 cm) in thickness. The housing 210 optionally also has a protective outer layer 225. The protective outer layer 225 resides external to the wall 212 and provides an additional thin layer of protection for the electronics.

The communication node 200 may be of any size practical for the downhole environment. For example, the communication node may be from about 12 to 16 inches in length as it resides along the tubular body. The housing 210 of the communication node may be 8 to 10 inches in length, and each opposing shoe 250 may be 2 to 5 inches in length. Further, the communication node may be about 1 inch in width and 1 inch in height. The base of the communication node may have a concave profile that generally matches the radius of the tubular body.

A bore 205 is formed within the wall 212. The bore 205 houses the electronics, such as a battery 230, a power supply wire 235, a transceiver 240, and a circuit board 245. The circuit board 245 will preferably include a micro-processor or electronics module that processes acoustic signals. An electro-acoustic transducer 242 is provided to convert acoustical energy to electrical energy (or vice-versa) and is coupled with outer wall 212 on the side attached to the tubular body. The transducer 242 may be in electrical communication with one or more sensors 232 and/or 234.

The sensor may be, for example, pressure sensors, temperature sensors, or microphones, or any other sensor as described herein or with reference to FIG. 2A. The sensor 232 and/or 234 sends signals to the transceiver 240 through a short electrical wire or through the printed circuit board 245. Signals from the sensor 232 are converted into acoustic signals using an electro-acoustic transducer 242, which are then sent by the transceiver 240 as part of the packet of information. For example, the sensor will measure a piece of data, such as a temperature measurement, strain measurement, acoustic noise data, geophone data, etc., the transducer then converts the piece of data (e.g., the temperature) into an acoustic waveform indicative of the data, which is then sent by the transceiver onto the next communication node.

In FIG. 2B, the sensor 232 resides within the housing 210 of the communication node 200. However, in some embodiments there may not be a sensor 232, and instead a sensor 234 may reside external to the communication node 200. The external sensor may be above or below the communication node 200 along the wellbore. In FIG. 2B, a dashed line is provided showing an extended connection between the sensor 234 and the electro-acoustic transducer 242.

While FIG. 2B illustrates sensors associated with the communication node 200, in the network illustrated in FIG. 1 it is not required that all of the communication nodes 180 possess or be associated with a sensor. That is, some communication nodes 180 may have sensors, while others may not and may simply be used to transmit information up and down the wellbore.

Returning to FIG. 2B, the communication node 200 also, optionally, includes a shoe 250. For example, the node 200 may include a pair of shoes 250 disposed at opposing ends of wall 212. Each of the shoes 250 provides a beveled face that helps prevent the node 200 from hanging up on an external tubular body or the surrounding earth formation, as the case may be, during run-in or pull-out. The shoes may have a protective outer layer 222 and an optional cushioning material under the outer layer 222.

As seen in FIG. 2B, the communication node has an independent power source 230. The independent power source 230 may be, for example, batteries or a fuel cell. Having a power source that resides within the housing of the communication nodes avoids the need for passing electrical connections through the housing, which could compromise fluid isolation.

In some embodiments, the power source may be a rechargeable power source, such as a rechargeable battery.

As described above with reference to FIGS. 1, 2A, and 2B, each communication node can have the capability of sending and receiving signals, so that the downhole wireless network is able to transmit data in a node-to-node arrangement from the subsurface to the surface. In preferred embodiments, the data transmitted between the nodes is represented by acoustic waves. In some embodiments, the acoustic telemetry data transfer is accomplished using multiple frequency shift keying (“MFSK”) modulation method. Although MFSK is well-suited for application in the downhole wireless networks described herein, its use is as an example and is not intended to be limiting. That is, it is known that various alternative forms of digital data modulation are available, for example, frequency shift keying (“FSK”), multi-frequency signaling, phase shift keying, pulse position modulation, and on-off keying.

Thus, signals generated by the electro-transducer within a communication node pass through the communication nodes' housing to the tubular body (such as the production or casing string), and propagate along the tubular body to other communication nodes. The data is then re-transmitted in a node-to-node arrangement up the wellbore until it reaches the topside communication node and the well operator. The re-transmitted signal represents the same sensor data originally transmitted by the first sensing communication node.

In some embodiments, the acoustic signal may be generated and received by magnetostrictive transducer(s) comprising a coil wrapped around a core as the transceiver. In some embodiments, the acoustic signal is generated and received by a piezo-electric ceramic transducer. In either case, the electrically encoded data is transformed into a sonic wave that is carried through the wall of the tubular body in the wellbore.

Acoustic telemetry along tubulars is characterized by multi-path or reverberation which persists for a period of milliseconds. As a result, a transmitted tone of a few milliseconds duration determines the dominant received frequency for a period of time of additional milliseconds. Preferably, the communication nodes determine the transmitted frequency by receiving or “listening to” the acoustic waves for a period of time corresponding to the reverberation time, which is typically much longer than the transmission time. The tone duration should be long enough that the frequency spectrum of the tone burst has negligible energy at the frequencies of neighboring tones, and the listening time must be long enough for the multipath to become substantially reduced in amplitude. For example, the tone duration may be 2 milliseconds (ms), and then the transmitter may remain silent for 48 ms before sending the next tone. The receiver, however, would listen for 50 ms (2+48) to determine each transmitted frequency, utilizing the long reverberation time to make the frequency determination more certain. Beneficially, the energy required to transmit data is reduced by transmitting for a short-period of time and exploiting the multi-path to extend the listening time during which the transmitted frequency may be detected.

For example, as described above, an MFSK modulation may be employed where each tone is selected from an alphabet of 16 tones, so that it represents 4 bits of information. With a listening time of 50 ms, for example, the data rate is 80 bits per second.

The tones are selected to be within a frequency band where the signal is detectable above ambient and electronic noise at least two nodes away from the transmitter node so that if one node fails, it can be bypassed by transmitting data directly between its nearest neighbors above and below. For example, the tones may be evenly spaced in period within a frequency band of from about 100 kHz to about 125 kHz. As another example, the tones may be evenly spaced in frequency within a frequency band of from about 100 kHz to about 125 kHz.

Preferably, the nodes employ a “frequency hopping” method where the last transmitted tone is not immediately re-used. This prevents extended reverberation from being mistaken for a second transmitted tone at the same frequency. For example, 17 tones are utilized for representing data in an MFSK modulation scheme; however, the last-used tone is excluded so that only 16 tones are actually available for section at any time.

Any extraneous noise in the signal can be moderated by using well-known conventional analog and/or digital signal processing methods. The noise removal and signal enhancement may involve conveying the acoustic signal through a signal conditioning circuit using, for example, a bandpass filter.

Returning to FIG. 1, each communication node is associated with a specific conduit or tubular member, and may be associated with a specific joint of pipe. That joint of pipe, in turn, has a known location or depth along the wellbore. Each acoustic wave as originally transmitted from a communication node will represent a packet of information. The packet will include an identification code that tells a receiver (such as receiver 170 in FIG. 1) where the signal originated, that is, which communication node 180 it came from. For example, the packet can include an amplitude value originally recorded by the communication node 180 for its associated joint of pipe. The packets of information are then relayed node-to-node from the communication nodes 180 in the subsurface to the one or more topside nodes 182 an on to the receiver 170.

As such, each signal defines a packet of information having at least an identifier (such as an acoustic amplitude value) for the subsurface communication node that originally transmitted the signal. When the signal reaches the receiver at the surface, the signal is processed. This involves identifying which communication node the signal originated from, and then determining the location of that communication node along the wellbore.

The data packet may further comprise data obtained from one or more sensors associated with the communication node. As described above, the communication node may contain or be associated with one or more sensors. The sensors may be, for example, fluid velocity measurement device, a temperature sensor, a pressure sensor, a fluid density sensor, a microphone, an ultrasound sensor, a Doppler shift sensor, a chemical sensor, an imaging sensor, an impedance sensor, an attenuation sensor, a fluid resistivity sensor, and/or other useful type of sensor. In general, the sensor sends signals to the transceiver which are converted into acoustic signals using an electro-acoustic transducer, that are then sent by the transceiver as part of the packet of information. Thus, the communication node may be configured to receive signals from the associated sensor and transmit signals indicative of readings taken by the sensor.

To conserve power, the communication nodes may be configured to operate in various modes, such as a sleep mode and an operational mode. For example, the communication node may include a sleep mode that is a low power, non-responsive energy saving state. The sleep mode may be a low energy mode, which limits the availability of the communication node to receive transmitted signals. The operational mode may be a mode of operation that involves running the processor in one or more of an active mode or a listening mode. The listening mode may involve monitoring for received signals, while the active mode may involve transmitting, obtaining measurement data, and/or storing measurement data from sensors.

The communication nodes may also communicate with other communication devices (other than the other communications nodes). The communication device may communicate with the communications nodes with low-frequency signals or high-frequency signals, and may be utilized to exchange data or instructions with the communication nodes. For example, the communication nodes may be configured to be able to communicate with a communication device such as a hydrophone, or other downhole tool.

When there is a failure along the downhole wireless communications network, it may be desirable to obtain the data from the network and also to repair the network. This failure could be due to an error in the programming of the software on the node, or it could be a hardware failure. The failure may be a local failure, involving only a few nodes, or may be a regional failure, where many nodes are affected. An example of a local failure may occur when two or more communications nodes do not communicate with each other after a certain number of attempts (e.g., three, or four, or five, or more failed attempts to communicate).

In some instances, the full system may also need to be re-evaluated when there are changes in the acoustic environment within the wellbore. For example, cementing, fracking, and/or injections within the well can alter the acoustic environment within the well. Also, over time simply producing hydrocarbons can alter the acoustic environment within the well. The changes in the environment can then lead to changes in the acoustic conditions along the tubular member, which can affect the reliability and accuracy of communications between the communications nodes. Thus, the communications nodes within the network may need to be re-programmed with different filters that aid in the removal of background noise (e.g., production noise) that did not exist when the network was first put in place.

The present methods and systems utilize a downhole tool, such as a downhole tool that comprise a communications device to either repair the network or to help collect data from the severed portion of the network. For example, the downhole tool may include an associated signal receiver. The signal receiver may be configured to receive the data signals from various communication nodes as the downhole tool passes the nodes in the wellbore.

As described above, the present methods and techniques may be useful for operating and maintaining downhole wireless networks, such as those described with reference to FIGS. 1 2A, and 2B. For example, FIG. 5 is an exemplary flow chart 500 in accordance with an embodiment of the present techniques. The flow chart 500 is a method and system for operating and maintaining a downhole wireless network. In general, the method may comprise detecting a failure in the downhole wireless network and using a communications device, such as a hydrophone, to correct the error and/or to bypass the malfunctioning communications nodes in the downhole wireless network.

While not illustrated in FIG. 5, the method may first comprise providing a downhole wireless network as described herein. The network may comprise a series of communication nodes that are attached to a tubular in the wellbore, where adjacent communication nodes are configured to communicate by acoustic signals transmitted through the tubular.

Once the downhole wireless network is provide, the method may comprise operating the downhole wireless network to communicate data signals from the subsurface to the surface. At block 502 a communication failure is detected in the downhole wireless network. The communication failure may be identified by the operator when data signals are no longer received below a certain point (or depth) of the wellbore. As such, the operator may conclude that one or more communication nodes in the network are malfunctioning.

At block 504 the location of the error is identified. Identifying the location of the error may entail examining the data packets to identify the deepest communication node (i.e., the communications node farthest from the surface) that originated a signal. For example, referring to FIG. 3A, the data packets that are received at the topside can be analyzed to determine that Node 24 is the deepest communication node from which a signal was received. Thus, the operator can determine that there is a communication error at Node 25.

At block 506 a downhole tool, such as a communications device, may be lowered into the wellbore to the location of the error. For example, a downhole tool that contains a communications device may be run into the wellbore. The downhole tool may be run into the wellbore using a working string (such as a coiled tubing string, a jointed working string, a slick line, or an electrical line) or may be an autonomous tool that is wireless. Thus, the downhole tool may be conveyable within the wellbore via a tubing string, coil tubing, wireline, electrical wireline, autonomously, or pumped in by a fluid. In some embodiments a downhole tool such as that illustrated in FIG. 4 may be used.

In preferred embodiments, the downhole tool allows for two-way communication with the subsurface communication nodes. For example, the downhole tool may be a long-range ultrasonic hydrophone that operates at a frequency of from 50-500 kHz. Preferably, the downhole tool is lowered through the production string and is able to communicate with a communications node that is exterior of the wellbore casing. In such instances, the downhole tool should be designed and configured such that is able to communicate through layers of cement, mud, the tubular (i.e., piping and/or casing), as well as the formation.

An exemplary downhole tool 400 that may be used is illustrated in FIG. 4. The downhole tool comprises a housing 408 that holds piezoelectric transducers and sensors 416, a power supply 414, a two-way communications transceiver 412, and an electronics board 410. Preferably, the housing holds a plurality of piezoelectric transducers and sensors 416 that are positioned around the housing, such that the plurality comprises at least one facing upwards, downwards, and sideways. The electronics board 410 provides for a transducer interface, control electronics, signal generation / processing, data and telemetry system diagnostics, and data logging capabilities. The downhole tool may be lowered into the wellbore via a wireline cable 406 which may be connected to a truck interface unit 404. The truck interface unit 404 may then have a wireless or wired connection to a control computer 402.

Returning to FIG. 5, the downhole tool comprising a communications device is lowered into the wellbore to the location of the error at block 506. Optionally, at block 508 the downhole tool can be used to diagnose or troubleshoot the type of error that is occurring with the communications node. For example, the downhole tool can be determined if the error is due to a power failure 510, a mechanical failure 514, or a programming / software failure 518.

If the error is determined to be caused by a power failure 510 or a low battery in a communications node, the downhole tool can be used to attempt to recharge the battery in the malfunction node. For example, at block 512, the downhole tool could be used to wirelessly recharge the battery. Alternatively, it could be determined to lower a different downhole tool into the wellbore that can recharge the battery in the communications node through electrical pulses sent through the wall of the casing.

If the error is determined to be caused by a programming or software failure 518, the downhole tool can be used to reprogram the malfunctioning communications node. For example, the downhole tool may wirelessly transmit a new program / software code to the malfunction node at block 520. This may be useful when there has been a change in the acoustic conditions within the wellbore, such that the communications node needs to be reprogramed to transmit at a different frequency or to use different frequency keys, etc.

Additionally, in some embodiments, the downhole tool may be used to reprogram a communications node to provide the communications node with new functionalities even if the communications node is currently functioning properly. For example, the communication node could be reprogramed to be associated with a new wireless sensor, and thus be programed to transmit data signals from the new sensor.

In some embodiments it may be determined that the error is a mechanical error 514 (e.g., a mechanical failure of the communication node's transceiver) that cannot be fixed. Similarly, it may be determined that the power failure 510 or software/programming failure 518 are such that they cannot be fixed. In such instances, the downhole tool can be used to heal the network by bridging the gap between functioning nodes at block 516.

Referring to FIG. 3B, the hydrophone may be lowered downhole to be near the malfunctioning nodes, Nodes 25 and 26. The hydrophone can then be used to collect data from Node 27 and transmit the data upstream to Node 24 from which it can be transmitted through the downhole wireless network to the surface. Alternatively, the hydrophone can collect the data from Node 27 and transmit the data up the wireline to the surface or use the low frequency capabilities of the hydrophone to acoustically transmit the data to the surface.

Referring to FIG. 5, hydrocarbon fluids may then be produce from the wellbore at block 522.

As described herein, the present methods and systems may be used to operate a downhole wireless network even though one or more communication nodes within the network have begun to malfunction. Further, the present methods and systems may additionally be used to reprogram nodes within the network, such that they are once again able to operate properly. In such a manner, the present methods and systems may be used to “heal” a damaged downhole wireless network. This can be advantageous as it can allow for the collection of data from functioning portions of the network that may be otherwise cut-off. Additionally, once the casing the communication nodes are placed on has been cemented into place, it is difficult if not impossible to physically access the nodes and repair them. As such, the present methods and systems can provide means for wirelessly correcting some problems and allowing the nodes to function again.

It should be understood that the preceding is merely a detailed description of specific embodiments of the invention and that numerous changes, modifications, and alternatives to the disclosed embodiments can be made in accordance with the disclosure here without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents. It is also contemplated that structures and features embodied in the present examples can be altered, rearranged, substituted, deleted, duplicated, combined, or added to each other. As such, it will be apparent, however, to one skilled in the art, that many modifications and variations to the embodiments described herein are possible. All such modifications and variations are intended to be within the scope of the present invention, as defined by the appended claims. 

1. A method for operating a downhole wireless network, comprising: providing a downhole wireless network, where the downhole wireless network comprises a plurality of communication nodes spaced along a wellbore and attached to an outer surface of a tubular within the wellbore, where the communication nodes are configured to transmit data signals as acoustic waves from node-to-node up the wellbore to the surface; detecting a communication error in the downhole wireless network, where data signals from at least one communication node is not received at the surface; identifying the location of the communication node that is causing the communication error; lowering a downhole tool comprising a communications device into the wellbore to the location of the error; transmitting data signals from a communication node lower than the location of the error to the downhole tool; and transmitting the data signals from the downhole tool to the surface.
 2. The method of claim 1, wherein each of the subsurface communication nodes comprises: a sealed housing; an electro-acoustic transducer and associated transceiver residing within the housing, where the transceiver is configured to relay signals from node-to-node up the wellbore, with each signal representing a packet of information that comprises (i) an identifier for the subsurface communications node that originally transmitted the signal and (ii) signals indicative of readings taken by one or more downhole sensors; and an independent power source residing within the housing providing power to the transceiver.
 3. The method of claim 1, wherein the communication nodes are spaced apart such that each joint of pipe in the tubular supports at least one communications node.
 4. The method of claim 1, wherein the communications nodes are spaced at an interval of from about 20 feet to about 40 feet.
 5. The method of claim 1, wherein each of the communication nodes is designed to receive acoustic waves at a first frequency and then transmit the acoustic waves at a second frequency up the wellbore to a receiver at the surface.
 6. The method of claim 1, wherein one or more sensors reside within the housings of selected communications nodes.
 7. The method of claim 1, wherein the electro-acoustic transducers within the selected communications nodes convert signals from the sensors into acoustic signals for the associated transceivers.
 8. The method of claim 1, wherein the downhole tool comprises a hydrophone.
 9. The method of claim 8, wherein the hydrophone is an ultrasonic hydrophone.
 10. The method of claim 8, wherein the hydrophone transmits signals at a frequency in the range of from 50 to 500 kHz.
 11. The method of claim 1, wherein the downhole tool transmits the data signals to the surface via a wireline.
 12. The method of claim 1, wherein the downhole tool transmits the data signals to the surface via long-range ultrasonic acoustic transmissions.
 13. The method of claim 1, wherein the downhole tool transmits the data signals to the surface by transmitting the data signals to a communication node above the location of the error and wherein the communication node then transmits the data signals in a node-to-node manner up the wellbore to the surface.
 14. The method of claim 1, further comprising using the downhole tool to determine the type of error that is occurring in the communication node.
 15. The method of claim 1, further comprising wirelessly transmitting a new program from the downhole tool to the malfunctioning communication node.
 16. A method for operating a downhole wireless network, comprising: providing a downhole wireless network, where the downhole wireless network comprises a plurality of communication nodes spaced along a wellbore and attached to an outer surface of a tubular within the wellbore, where the communication nodes are configured to transmit data signals as acoustic waves from node-to-node up the wellbore to the surface; lowering a downhole tool comprising a communications device into the wellbore to a location associated with at least one identified communication node; transmitting signals from the downhole tool to the identified communication node, whereby the signals operate to re-program the communication node.
 17. The method of claim 16, wherein the signals from the downhole tool operate to re- program the communication node with a new filter to better filter out background noise. 